Isoniazid is NOT given in:

Ref: KD Tripathi, 7th ed. pg. 767* INH is hepatotoxic and is avoided in pre-existing liver disease* Isoniazid is an essential component of all anti-tubercular regimens. It is primarily tuberculocidal.* Fast multiplying organisms are rapidly killed, but quiescent ones are only inhibited.* The most common mechanism which confers high level INH resistance is by mutation of the catalase-peroxidase (KatG) gene.* INH resistance may also involve mutation in the inhA or kasA genes.Adverse effects:* Peripheral neuritis is the most important dose- dependent toxic effects (slow acetylators).# Pyridoxine given prophylactically (10mg/day) prevents the neurotoxicity even with higher doses.# Prophylactic pyridoxine must be given to diabetics, chronic alcoholics, malnourished, pregnant, lactating and HIV infected patients, but routine use is not mandatory.* Hepatitis, a major adverse effect of INH, (seen commonly in fast acetylators) more common in older people and in alcoholics is also a well-known side effect of the drug.* Other adverse effects: Xerostomia, Allergic reactions, decrease seizure threshold.* Safest ATT in renal disease patients: Rifampicin* ATT which has no/least hepatotoxicity: Ethambutol and Streptomycin